1. Field of the Invention
The present invention relates to a method and apparatus for determining optical writing power for recording data on a recording medium such as an optical disk.
2. Description of the Related Art
FIG. 1 shows areas allocated in a CD-RW disk with emphasis on the PCA (power calibration area) used for determining optical writing power. A general optical disk recording apparatus performs an OPC (optimal power calibration) operation on the PCA of an optical disk to determine a writing power optimal for the optical disk recording apparatus and the optical disk before actually recording data in the program area of the optical disk.
As shown in FIG. 1, the OPC operation records test data of a predetermined length in the test area of the PCA several times with varying writing powers and reproduces the recorded test data to determine the writing power which results in the best-quality signals when the test data is reproduced, thereby determining the optimal writing power. The test area in the PCA is organized into 100 partitions, each of which can accommodate 15 ATIP frames. Each OPC operation records 15 frames in one of the 100 partitions. The 15 frames are recorded with 15 different writing powers.
Because the PCA is organized into 100 partitions, the optical disk can allow up to 100 new OPC operations. In other words, the first 100 OPC operations are performed in partitions wherein no data has been recorded before.
After each test recording is completed, null data of a size of one frame is written in the count area of the PCA to indicate that 1 OPC operation is conducted.
If the optimal writing power is determined after the OPC operation, data (i.e., not the test data) is recorded in the program area (data area) of the optical disk with the determined optimal writing power afterwards.
It is common that a rewritable optical disk is used in such a way that data recorded in the data area of the optical disk can be overwritten with new data if the old data is not necessary. According to this practice, when the old data recorded in a particular area of the data area is overwritten with the new data, the old data is DC erased first before the new data is recorded in the same data area. But, the quality of the recording layer of the rewritable disk is deteriorated with the repeated DC erasing and data recording operations. Therefore, the property of the rewritable optical disk at the moment of a first data recording in a data area is different from that at the moment of the overwrite in the data area. As a result, it is desirable that the writing power for overwriting the old data be different from the writing power determined at the initial data recording even for the same location of the optical disk.
According to the related art, however, when overwriting of data is performed in a data area of an optical disc, the OPC operation for determining an optimal writing power in that data area is performed in the test area of the PCA wherein no test data has been recorded before, if the number of data recording operations conducted thus far is less than 100. Thus the writing power determined in such a way leads to the deterioration of recording quality because the determined writing power is not suitable for data areas wherein DC erasing operations have been performed repeatedly.